The principle of least action, a law of nature

Mass makes its way instant by instant but does it follow a preordained path?

In 1661 Pierre de Fermat thought a bending of a ray of light as it passes from air into water or glass occurs because it is the fast path. A lifeguard can run at a faster speed than he can swim so he should estimate the path of least time to a swimmer because the shortest path, a straight line, is not the fastest path to a drowning swimmer. Fermat thought light must travel slower in denser media.

Later, Newton thought he proved the opposite. Fermat's principle of simplicity is correct. Theology and physics had not yet distanced themseleves so scientists found it natural to ask "what sort of universe would god make?' Even Einstein would doubt that god played dice with the world at a time when he felt a need to balance between the literal believers in god and his disbelieving professional colleagues.

We now know the more competently science performs is when it has no need for a god. God does not intervene but is rather oblivious or nonexistant; it was Newton's second law where force was equal to the mass times the acceleration. However, Pierre-Louis de Maupertuis discovered a way of seeing such paths. In his scheme, a planet's path has a most economical logic that cant be seen from the vantage point of someone merely adding and subtracting the forces at work instant by instant.

Joseph lagrange showed that the paths of moving objects are always the most economical. These paths minimize a quantity called action. Action is a quantity based on the object's velocity, mass and space it traverses. A planet chooses the best of all possible paths as if god was leaving his stamp.

Where Newton's methods left a feeling of comprehension, the scientists were left with a sense of mystery with minimum principles. Quantum mechanics was the answer.